Sea eagles demonised, again

It seems barely a month goes by without someone trying to demonise white-tailed eagles in Scotland.

This time it’s the handiwork of Telegraph ‘journalist’ Auslan Cramb, with an article headlined:

Sea eagles eat more lamb than fish, despite their name, according to research.

We really shouldn’t be surprised that this scaremongering drivel has been churned out by Cramb. He’s the same ‘journalist’ who in October falsely claimed that ‘Wind turbines have killed more birds of prey than persecution this year‘ – a claim we demonstrated was false here.

His latest claim is based on the results of a series of photographs that were taken at a white-tailed eagle’s nest in Argyll between January and July this year. Yes, that’s right, footage from a single nest, filmed during a single period. Hardly representative, is it?

According to SNH, this eagle pair brought in 117 prey items to the nest. 67 of these (57%) were unidentifiable. Of the items that were identifiable, 21 items were mammals, 14 were birds, 7 were fish and ‘8 or 9’ were lambs.

So this camera at this particular eagle’s nest, during this particular period, filmed one or two more lambs than fish. Does that justify the scaremongering headline that sea eagles eat more lamb than fish? Hardly. But then a headline such as ‘Pair of sea eagles enjoy a varied, generalist diet’ isn’t really what the raptor killers want the public to believe, is it?

The article also fails to explain that these ‘8 or 9’ lambs could well have been taken as carrion (i.e. the lambs were already dead and the eagles simply scavenged the carcasses).

To try and pass these results off as a conclusive scientific study is pure desperation. It’s what’s known as ‘utter bollocks’ in scientific terms. Trying to determine raptor diet using a single method (such as nest camera footage) is a well-known problem that is beset with bias. There are numerous methods of obtaining such data (e.g. analysis of regurgitated pellets, analysis of prey remains, camera footage) and considerable research has shown that a combination of methods should be used, rather than a single one. The additional issue of using a sample size of one (nest) is just laughable. It is also well known that the diet of individual eagle pairs can vary across years in western Scotland, as reported by sea eagle experts Mike Madders and Mick Marquiss in 2003.

The most recent, properly conducted, scientific study on white-tailed eagle diet in western Scotland was published in 2013. That study included the analysis of pellet and prey remains from 16 sea eagle nests on Skye, Mull, Lewis and Harris, over an eight year period. The study found that 49.6% of the eagles’ diet comprised seabirds, 19.2% sheep, 13.4% lagomorphs and 6.1% fish. However, the authors acknowledged that the estimation of fish in the eagles’ diet was probably under-estimated due to the methods of dietary analysis that they used.

The purpose of installing the camera at the Argyll eagle pair’s nest was part of an on-going effort to understand the conflict between sea eagles and farming/crofting interests in western Scotland. This is a long-standing and controversial issue that we’ve blogged about a lot (here is an example). It would appear that if farmers/crofters want to deter sea eagles there’s a simple solution – attach a small black plastic box to the lamb’s neck (about the size of a matchbox). Why? Because a load of lambs were radio tagged during an earlier study into alleged lamb-killing eagles and the results showed that not one single lamb was killed by an eagle. The crofters claimed the eagles had been ‘put off’ because of the radio collars/tags. (They also claimed that the eagles had been given supplementary food during the study period, and that some eagles had been ‘bird-napped’ to remove them from the study area!).

UPDATE 22nd December 2014: RSPB Scotland responds to this idiotic Telegraph article here

It’s also reproduced here:

22 Dec 2014

Senior Conservation Policy Officer, Richard Evans, has this response to a recent article on sea eagles in the Daily Telegraph.

Bad science (or never let the truth get in the way of a “good” story)

Last month, we blogged [1] about a piece in the Daily Telegraph[2] that suggested that more birds of prey were killed by wind turbines than by gamekeepers.  We pointed out that the paper had fallen into the trap of selection bias[3], because birds killed by turbines were far more likely to be reported than birds killed by gamekeepers.

Well, the Telegraph is at it again, this time beavering away at the hoary (but seasonal) old chestnut of white-tailed (sea) eagle diet[4].  According to the press release[5] from SNH and partners (Forest Enterprise Scotland, National Farmers Union of Scotland and RSPB Scotland), a camera placed by FCS at a sea eagle nest on their land to record prey brought in by the adults showed:

“The sea eagles brought a total of 117 prey items to the nest between January and July. Analysis confirmed that 67 items were unidentifiable, 21 were mammals, 14 were birds, 7 were fish, and either 8 or 9 were lambs.”

The Telegraph headlined their story: “Sea eagles eat more lamb than fish, despite their name, according to research.”  “Eight or nine” is more than seven, so the Telegraph is right this time, surely?

Ummm, not when the data are subject (just like the wind turbine and illegal persecution data) to selection bias.  Let’s look at those figures a little more closely.  Firstly, well over half the items recorded carried to the nest by cameras were “unidentifiable”.  This is not particularly surprising.  In the experience of most RSPB staff with sea eagle nest watching experience, including the use of cameras, it can be very difficult to identify some prey items, particularly if they are small and nondescript in colour.  A bit like most inshore fish and many bird species known to be taken by sea eagles.  And not in the least like lambs, which (as many RSPB staff with sea eagle nest watching experience can confirm) tend to appear very obviously large and white, and on camera also woolly.

But eight (or nine) is still more than seven, right?  Actually, almost certainly wrong when the fractionally smaller category (7 items) is much more difficult to identify than the marginally larger one (8 or 9 items); and when (as here) most items were unidentified, and likely to include many from the difficult-to-identify category (here fish; and previously, illegally-killed birds of prey).

But it gets worse.  This time the Telegraph is guilty of a special type of selection bias commonly known as hasty generalisation[6].  As any fool knows, you can’t (or at any rate shouldn’t) generalise from a sample of one.  But that is precisely what the Telegraph article does, by applying the (incorrectly interpreted) results using a single technique, from a single year and a single site, to all sea eagles everywhere.

We have known for a long time[7] that some sea eagles take some lambs, some of which are taken alive (but at least some of which in turn are in poor condition).  We also know that there’s great variation between the diets of different pairs. So while the latest camera deployment tells us something about the diet of this pair in 2014 (mainly that we don’t actually know most of what they ate), it doesn’t allow the wild extrapolation indulged in by the Telegraph in this article.

Which all goes to show that you can take a horse to water, but you can’t make him think. Or something like that.